1. Field of the Invention
The present invention relates to an apparatus for inspecting the coating state of cream solder coated on a printed circuit board (PCB), and a method thereof.
2. Description of the Related Art
Cream solder or solder paste is coated on a PCB to mount electronic parts such as a semiconductor chip on the PCB. That is, a metal mask having holes at predetermined positions is placed on the PCB, and is coated with cream solder in a paste state by a conventional cream solder printing apparatus. The coating state of cream solder affects subsequent processes of mounting electronic parts. Thus, to improve reliability of a subsequent process, a process for inspecting the coating state of cream solder on a PCB is needed.
FIG. 1 is a view schematically showing the structure of a conventional apparatus for inspecting cream solder coated on a PCB.
Referring to the drawing, the conventional apparatus includes a camera 13 for capturing a picture of a PCB 12 onto which cream solder 11 is coated, and an illumination system 14 disposed above the PCB 12 for emitting light onto the cream solder 11 on the PCB 12 at predetermined angles.
When the illumination system 14 illuminates the cream solder 11 coated on the PCB 12 at predetermined angles, as shown in FIG. 2, light emitted from the illumination system 14 reflects from a round edge portion 11a of the cream solder 11 to proceed toward the camera 13. Accordingly, in an image captured by the camera 13, the edge portion 11a of the cream solder 11 is brighter than other areas . The image is binary-processed, i.e., a portion of the image brighter than the reference is processed into xe2x80x9c1xe2x80x9d and a portion thereof darker than the reference is processed into xe2x80x9c0xe2x80x9d. Consequently, the edge portion 11a of the cream solder 11 is represented by a line so that the coating state of the cream solder 11 can be recognized. Thus, by inspecting the edge shape of cream solder using the above binary-processed image, a defective coating state of cream solder such as a defective coating position, or excessive or insufficient coating, can be detected.
However, in the conventional inspection of cream solder on a PCB, as a defective coating state of cream solder is determined by simply inspecting the shape of the edge of the cream solder, it is hot possible to determine the thickness of cream solder and the coating defectiveness inside the edge of the cream solder. Thus, reliability in the inspection is lowered.
To solve the above problems, it is an objective of the present invention to provide an apparatus and method of inspecting cream solder on a PCB, by which not only a coating position error of cream solder coated on the PCB but also a defective coating state of the cream solder can be detected.
Accordingly, to achieve the above objective, there is provided an apparatus for inspecting cream solder on a PCB comprising: a camera for capturing an image is of cream solder coated on the upper surface of said PCB; a first illuminator for illuminating said cream solder such that the light reflected from an edge of said cream solder forming an angle with respect to the upper surface of said PCB, proceeds toward said camera; a second illuminator for illuminating said cream solder such that the light reflected from the upper surface of said cream solder parallel to the upper surface of said PCB, proceeds toward said camera; and a controller for controlling said camera,,said first and said second illuminators, and for processing the image captured by said camera into a binary image.
It is preferred in the present invention that said first and said second illuminators operate selectively, the image captured by said first illuminator is binary-processed by said controller so that the edge of said cream solder only is formed as an image, and the image captured by said second illuminator is binary processed by said controller so that the coating area of said cream solder only is formed as an image.
It is also preferred in the present invention that said first illuminator is formed of a plurality of light emitting diodes which emit light of green or blue wavelength in a ring shape, and said second illuminator is formed of a plurality of light emitting diodes which emit light of red wavelength in a ring shape.
According to another aspect of the present invention, there is provided a method of inspecting cream solder on a PCB, comprising the steps of: (a) capturing an image of the light emitted by a first illuminator and reflected from an edge surface of said cream solder coated on said PCB, using a camera; (b) forming an image of only the edge of said cream solder by binary-processing the image captured in said step (a); (c) determining defectiveness in the coating position of said cream solder by comparing edge coordinates of said cream solder with reference coordinates; (d) capturing an image of the light emitted by a second illuminator and reflected from the upper surface of said cream solder coated on said PCB, while said first illuminator is turned off; (e) forming an image of only an area where said cream solder is coated, by binary-processing the image captured in said step (d); and (f) determining defectiveness in the coating state inside the edge of said cream solder by combining the image of the edge obtained in said step (b) and the image of the coating area obtained in said step (e).
It is preferred in the present invention that, in said step (b), the light reflected by the edge and brighter than a first reference brightness is processed into xe2x80x9c1xe2x80x9d, while the light darker than said first reference brightness is processed into xe2x80x9c0xe2x80x9d, so that said image of the edge is obtained.
It is also preferred in the present invention that, in the step (e), the light reflected by the area where the cream solder is coated and brighter than a second reference brightness and darker than a third reference brightness is processed into xe2x80x9c1xe2x80x9d, while the light reflected by the PCB and the area where the cream solder is not coated, and either darker than the second reference brightness or brighter than the third reference brightness is processed into xe2x80x9c0xe2x80x9d, so that the image of the area where the cream solder is coated is obtained.